Position detector and position indicator

ABSTRACT

A position detector includes a tablet and a position indicator, which includes a coil and configured to continuously transmit a coil-based signal to the tablet as a position signal and to intermittently transmit the coil-based signal to the tablet as a non-positional signal. The tablet is configured to detect a position on its surface pointed to by the position indicator by detecting the continuously-transmitted coil-based signal, and to determine non-positional information regarding the position indicator (e.g., pen pressure, pen ID, etc.) by detecting the intermittently-transmitted coil-based signal. The position indicator further includes position indicator control circuitry configured to control the position indicator to: (i) receive an indicator control signal from the tablet; (ii) based on the received indicator control signal, select one type of non-positional information from among multiple types of non-positional information regarding the position indicator; and (iii) transmit the selected one type of non-positional information to the tablet.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(a) ofJapanese Patent Application No. 2009-240727, filed Oct. 19, 2009, theentire content of which is being incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a position indicator and a positiondetector which is configured to detect multiple types of informationstored on a position indicator side including, for example, the positionindicator's specific ID or the like, and information regarding a penpressure or the like which is obtained in accordance with the use of theposition indicator.

BACKGROUND

A position detector called a pen tablet has been developed as one ofpointing devices used for photograph processing, illustration creation,or the like, on a computer apparatus. A pen tablet is generally composedof an approximately tabular position detector portion (hereinafterreferred to as a “tablet”), and a pen-like dedicated position indicatorwhich a user manipulates on the tablet.

In one such (pen tablet) position detector based on an electromagneticinduction system, a resonance circuit is provided in a positionindicator, and a reflected signal from the position indicator resonatingwith a signal transmitted from a tablet is detected by the tablet, tothereby obtain a position on the tablet as indicated by the positionindicator (for example, refer to Japanese Patent Laid-Open No.S63-70326).

In addition, there is also proposed a position detector having a form inwhich a tablet is integrated with a display device such as a liquidcrystal panel, whereby a position displayed on a screen is directlyinputted with a position indicator such as an electronic pen (forexample, refer to Japanese Patent Laid-Open No. 2002-215317).

Still further, a position detector is proposed in which a positionindicator is associated with not only its specific ID information andpen pressure information, but also with other multiple types ofinformation, of which necessary information can be selected and acquiredin accordance with an instruction issued from a tablet (for example,refer to Japanese Patent Laid-Open No. H7-200137).

Yet another position detector is proposed in which a power source isprovided in a position indicator to transmit a signal, and a transparentsensor tablet including a coil made of material having a highresistance, such as an ITO (Indium Tin Oxide) film, is disposed on afront surface of a liquid crystal panel (for example, refer to JapanesePatent Laid-Open No. 2007-257359).

SUMMARY OF THE INVENTION

In the existing position detectors, such as the one disclosed inJapanese Patent Laid-Open No. 2007-257359, since the signal from theposition indicator is detected by the loop coil made from the ITO filmformed on the transparent glass surface, it is possible to dispose thesensor tablet on the front surface of the display device. For thisreason, it becomes unnecessary to disassemble the liquid crystal panelin the manufacturing process to include the tablet in the positiondetector, which in turn enhances the interchangeability (compatibility)of the display device in design. In addition, since a power source isprovided in the position indicator in order to transmit a signal, itbecomes possible to increase the strength of the signal from theposition indicator. Thus, the position detector does not suffer muchinfluence by the noise radiated from the display device, and can stablydetect the coordinates of the position indicator on the tablet.

However, in the position detector such as the one as shown in JapanesePatent Laid-Open No. H7-200137, multiple types of information includingthe position indicator's specific ID and the like are associated withthe position indicator to allow for their detection by the tablet, allof those types of information need to be transmitted. As a result, atransfer speed is largely reduced.

According to one aspect, the present invention has been made in light ofthe problem described above. One embodiment of the present inventionprovides a position detector, wherein a power source is provided in aposition indicator in order to transmit a signal. Multiple types ofinformation including a specific ID and the like are set in the positionindicator, and a tablet can select and acquire necessary information outof these multiple types of information. According to another aspect ofthe present invention, even in the case of a large display device, thesensor tablet can be disposed on a front surface thereof.

According to yet another aspect of the present invention, a low-powerconsumption position indicator is provided, in which a battery as apower source provided in the position indicator needs not be exchangedor charged frequently.

In one embodiment, a position detector of the present invention includesa position indicator including a power source and configured tointermittently transmit a position indication signal to a tablet at apredetermined timing; and the tablet configured to detect a position onits surface pointed to by the position indicator by receiving theposition indication signal.

The position indicator further includes an information storing sectionconfigured to store therein multiple types of information; a controlsignal receiving circuitry configured to receive a control signaltransmitted thereto from the tablet; an information selecting circuitryconfigured to select one type of information from among the multipletypes of information stored in the information storing section inaccordance with a content of the control signal; and an informationtransmitting circuitry configured to transmit the one type ofinformation selected by the information selecting circuitry to thetablet.

The tablet includes a position signal receiving circuitry configured toreceive a position indication signal from the position indicator; atiming information extracting circuitry configured to extract thepredetermined timing from the position indication signal; and a controlsignal transmitting circuitry configured to transmit a control signal tothe position indicator. In the tablet, the position indication signalintermittently transmitted from the position indicator is received bythe position signal receiving circuitry, and the control signal istransmitted from the tablet to the position indicator synchronously withthe predetermined timing extracted by the timing information extractingcircuitry.

In other words, the tablet extracts the predetermined timing from theposition indication signal transmitted from the position indicator.Then, the tablet transmits the control signal to the position indicatorsynchronously with the extracted predetermined timing and, at the sametiming, the position indicator activates a receiving circuit.

Effects of the Invention

According to various embodiments of the present invention, since acontrol signal from the tablet is suitably amplified, even when thecontrol signal from the tablet is a weak signal, the control signal canbe reliably received by the position indicator. Thus, even when a loopcoil of the tablet is composed of either a transparent electrode such asan ITO film or a material having a high resistance value, the tablet canselect, based on the control information, the necessary information fromamong multiple types of information stored in the position indicator.For this reason, the transfer speed of the information from the positionindicator to the tablet is not reduced, since only the necessaryinformation can be obtained.

In addition, according to various embodiments of the present invention,since the control signal is transmitted from the tablet synchronouslywith the timing for the signal transmission from the position indicator,the control signal can be reliably transmitted/received during a shortperiod of time. For this reason, it is possible to further increase thetransfer speed of the information from the position indicator to thetablet.

In addition, according to various embodiments of the present invention,since the signal transmission from the position indicator is stoppedwhen the position indicator does not exist on a tablet, the powerconsumption of the position indicator can be reduced, and its batteryneed not to be exchanged or charged frequently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a position detector according to a firstembodiment of the present invention.

FIG. 2 is an external view of a position indicator according to thefirst embodiment of the present invention.

FIG. 3 is a block diagram showing an internal configuration of theposition indicator according to the first embodiment of the presentinvention.

FIG. 4 is a perspective exploded view showing a construction of a tabletaccording to the first embodiment of the present invention.

FIG. 5 is a block diagram showing an internal configuration of thetablet according to the first embodiment of the present invention.

FIG. 6 is a timing chart showing operations of the position indicatorand the tablet when a command of “101” is transmitted from the tablet,according to the first embodiment of the present invention.

FIG. 7 is a timing chart showing operations of the position indicatorand the tablet when a command of “100” is transmitted from the tablet,according to the first embodiment of the present invention.

FIG. 8 is a timing chart showing operations of the position indicatorand the tablet when a command of “110” is transmitted from the tablet,according to the first embodiment of the present invention.

FIG. 9 is a timing chart showing an initial operation of a first exampleof the first embodiment of the present invention.

FIG. 10 is a timing chart showing an initial operation of a secondexample of the first embodiment of the present invention.

FIG. 11 is a partial cross sectional view showing a construction of aposition indicating portion of a position indicator in a secondembodiment of the present invention.

FIG. 12 is a block diagram showing an internal configuration of theposition indicator according to the second embodiment of the presentinvention.

FIG. 13 is a timing chart showing operations of the position indicatorand the tablet when the command of “110” is transmitted from the tablet,according to the second embodiment of the present invention.

FIG. 14 is a partial cross sectional diagram showing a construction of aposition indicator according to a third embodiment of the presentinvention.

FIG. 15 is a block diagram showing an internal configuration of theposition indicator according to the third embodiment of the presentinvention.

FIG. 16 is a block diagram showing an internal configuration of a tabletaccording to the third embodiment of the present invention.

FIG. 17 is a timing chart showing an initial operation of the thirdembodiment of the present invention when a pen tip side of the positionindicator is placed on the tablet.

FIG. 18 is a timing chart showing a pen coordinate (pen position)/penpressure detecting operation of the third embodiment of the presentinvention when the pen tip side of the position indicator is placed onthe tablet.

FIG. 19 is a timing chart showing an initial operation of the thirdembodiment of the present invention when an eraser side of the positionindicator is placed on the tablet.

FIG. 20 is a timing chart showing a pen coordinate/pen pressuredetecting operation of the third embodiment of the present inventionwhen the eraser side of the position indicator is placed on the tablet.

DESCRIPTION OF THE INVENTION

Hereinafter, embodiments for carrying out the invention will bedescribed. It is noted that the description will be given below inaccordance with the following order.

1. First Embodiment (basic constitution example).

2. Modifications to the First Embodiment.

3. Second Embodiment (example in which a position indicator havingrotational angle information is used).

4. Third Embodiment (example in which a position indicator including apen tip and an eraser is used).

1. First Embodiment Description of External Appearance of a PositionDetector

FIG. 1 shows an external view of an embodiment of a position detector 10of the present invention. The position detector 10 according to thisembodiment is composed of a pen-shaped position indicator 1 and a tablet2.

The position indicator 1 is used on a position detection area 2 a of thetablet 2. A position (coordinates) indicated by the position indicator 1can be detected on the position detection area 2 a. In addition, theposition indicator is provided with a side lever (hereinafter referredto as “a slider”) 1 cb which can be moved vertically in a longitudinaldirection of the position indicator 1. Thus, a color, a thickness, orthe like of a pen can be set by adjusting a position of the slider 1 cb.In addition, the position indicator 1 can detect information regardingthe pen pressure applied to its pen tip portion (e.g., by the tabletsurface). Moreover, specific ID information used to individuallyidentify the position indicator 1 is stored in the position indicator.

In this embodiment, information regarding a position of the slider 1 cb(hereinafter referred to as “slider information”), pen pressureinformation, the ID information individually assigned to the positionindicator 1, and the like, are transmitted from the position indicator 1to the tablet 2 for a period of time different from a period of timeallocated for coordinate detection during which the tablet detects theposition indicated by the position indicator.

The tablet 2 is connected to an external computer apparatus (not shown).The tablet detects the coordinate position indicated by the positionindicator, and outputs the detected coordinate information, as well asinformation regarding the pen pressure and the like, to the computerapparatus. The computer apparatus executes necessary processing based onthe coordinate information, information regarding the pen pressure, andthe like, as received from the tablet 2.

In the tablet of this embodiment, a tablet sensor for detecting a signalfrom the position indicator is constructed in the form of a plurality oftransparent loop coils (not shown) composed of an ITO (Indium Tin Oxide)film. These transparent loop coils are disposed on a display portion 2 bcomposed of a liquid crystal panel and the like. When commands thatrequest various types of information are transmitted from the tablet 2to the position indicator 1, each of the command signals which aretransmitted becomes weak because the resistance value of the transparentloop coils is as high as several kilo-ohms to several tens of kilo-ohms.

For this reason, in this embodiment, the signal received by the positionindicator 1 from the tablet 2 is amplified, thereby making it possibleto properly detect the presence or absence of the signal. At this time,the commands transmitted from the tablet side can be expressed as achronological series of the presence or absence of a signal. Also, theoperational timing is matched between the position indicator and thetablet, to allow for precise transmission/reception of each of thecommands in a short period of time. The details of these operations willbe described later.

[Configuration of a Position Indicator]

Next, a configuration of the position indicator will be described withreference to FIG. 2. The position indicator has a pen-like shape.Reference symbol 1 b designates a pen rod (core). A tip portion of therod 1 b protrudes from a main body 1 a. The position indicator is usedto contact a tablet surface with the tip portion of the rod 1 b as a“pen tip.” Reference numeral 12 designates a hollow-shaped coil. The rod1 b extends completely through the coil 12. In addition, avariable-capacitance capacitor 23 is disposed on a side of the rod 1 b,which is opposite to the tip portion of the rod 1 b.

The variable-capacitance capacitor 23 changes its capacitance inaccordance with a magnitude of the pen pressure applied to the rod 1 b.A load applied to the variable-capacitance capacitor 23 is detected asthe pen pressure information by a pen pressure detecting circuit 21,which will be described later.

A groove 1 ca having a predetermined length in a longitudinal directionis provided in the main body 1 a. A slider 1 cb which is slidablebetween one end portion and the other end portion of the groove 1 ca ismounted to the groove 1 ca. Analog information on the movement of theslider 1 cb on the groove 1 ca is detected by a slider detecting circuit22, which will be described later.

FIG. 3 is a block diagram showing an example of an internalconfiguration of the position indicator. The position indicator isprovided with an oscillation circuit 11, a coil 12, a control circuit13, an amplifying circuit 14, a switch 15, a detecting circuit 16, acomparator 17 as a signal strength determining portion, aserial-to-parallel converting circuit 18 (hereinafter referred to as “anS/P converting circuit 18”), a switching circuit 19, an ID storingmemory 20, a pen pressure detecting circuit 21, a slider detectingcircuit 22, a clock generating circuit 25, and a power source 26.

The oscillation circuit 11 is a circuit which is operated together withthe coil 12 in accordance with an oscillation control signal Sc suppliedthereto from the control circuit 13, thereby generating a coil signal Sdhaving a predetermined frequency in the coil 12. The coil 12 generatesan AC magnetic field in accordance with the coil signal Sd. The tabletdetects the AC magnetic field generated from the coil 12 of the positionindicator, thereby obtaining the information regarding the coordinatesindicated by the position indicator, the pen pressure, and the like.

The control circuit 13 carries out control for the portions that formthe position indicator. Specifically, the control circuit 13 suppliesthe oscillation signal Sc to the oscillation circuit 11 described above,supplies an S/P conversion clock Sh to the S/P converting circuit 18which will be described later, supplies a continuous amount detectionpulse Ss, a continuous amount sending clock Sw, and the like, to the penpressure detecting circuit 21 and the slider detecting circuit 22 whichwill be described later, and the like. Details of these various kinds ofcontrol signals will be described later. A CPU (Central Processing Unit)can be used as the control circuit 13.

The amplifying circuit 14 is connected to the coil 12 through the switch15, and amplifies the signal induced in the coil 12 by the tablet. Thedetecting circuit 16 outputs a voltage corresponding to a level of theoutput signal from the amplifying circuit 14. The comparator 17 detectswhether or not the output voltage from the detecting circuit 16 is equalto or greater than a given voltage, and outputs a detection result as adigital signal.

The S/P converting circuit 18 reads the digital signal outputted fromthe comparator 17 at every cycle of the S/P conversion clock Sh suppliedthereto from the control circuit 13, and converts the read result intoparallel data, thereby outputting a resulting parallel data to theswitching circuit 19. In this embodiment, the S/P converting circuit 18outputs a 3-bit selection signal Sk.

The switching circuit 19 selects any one of the ID storing memory 20,the pen pressure detecting circuit 21, and the slider detecting circuit22 in accordance with a selection signal Sk outputted thereto from theS/P converting circuit 18, and supplies a signal from the selectedcircuit to the control circuit 13.

The ID storing memory 20 is composed of a semiconductor memory or thelike, and stores therein ID numbers individually assigned to theposition indicators. The pen pressure detecting circuit 21 detects thepen pressure applied to the rod 1 b (refer to FIG. 2), and outputsinformation regarding the pen pressure thus detected in the form of adigital value. The slider detecting circuit 22 detects sliderinformation of the slider 1 cb and outputs the slider information thusdetected in the form of a digital value.

Each of the pen pressure detecting circuit 21 and the slider detectingcircuit 22 is operated in accordance with the continuous amountdetection pulse Ss supplied thereto from the control circuit 13. Thecontinuous amount detection pulse Ss is a signal used to specify aperiod of time during which a continuous amount, such as the penpressure or the information regarding an operational amount of theslider 1 cb, is detected. In this embodiment, the continuous amountdetection pulse Ss is supplied during a period of time for continuoustransmission, which will be described later.

A resistor 211, a variable-capacitance capacitor 212, a comparator 213,an AND gate 214, a counter circuit 215, and a P/S converting circuit 216are included in the pen pressure detecting circuit 21.

The variable-capacitance capacitor 212 and the resistor 211 compose atime constant circuit. When the continuous amount detection pulse Ss isinputted to the time constant circuit, a signal St is outputted whoserising speed (rate of rise) is changed in accordance with a capacitanceof the variable-capacitance capacitor 212.

The comparator 213 has a given threshold, and converts the signal Stinto a digital signal in accordance with the threshold set therein. TheAND gate 214 has one inverting input and one non-inverting input. Anoutput signal from the comparator 213 is applied to a terminal on theinverting input side, and the continuous amount detection pulse Ss isapplied to a terminal on the non-inverting input side. By adopting sucha configuration, a pen pressure detection signal Su, whose pulse widthis changed in accordance with the pen pressure applied to thevariable-capacitance capacitor 212, is outputted from the AND gate 214.

The counter circuit 215 is provided with an enable terminal EN, a clockinput terminal CK, and a reset terminal R. A pen pressure detectionsignal Su outputted from the AND gate 214 is inputted to the enableterminal EN, and a coil signal Sd from the oscillation circuit 11 issupplied to the clock input terminal CK. Also, the continuous amountdetection pulse Ss is inputted to the reset terminal R.

The counter circuit 215 counts the coil signal Sd inputted to the clockinput terminal CK only during a period of time of the pulse width of thepen pressure detection signal Su supplied to the enable terminal EN, andoutputs a count value to the P/S converting circuit 226. It is notedthat during a period of time when the continuous amount detection pulseSs inputted to the reset terminal R is held at a Low level, the countvalue by the counter circuit 215 is reset. Since in this embodiment, thepen pressure information is expressed in the form of data of 10 bit, thedata outputted by the counter circuit 215 also has 10 bits. It is notedthat although in this embodiment, the pen pressure information isexpressed in the form of 10 bits, the number of bits is by no meanslimited thereto.

The P/S converting circuit 216 fetches the 10-bit data transmittedthereto from the counter circuit 215 at a rise timing of the continuousamount detection pulse Ss supplied thereto from the control circuit 13.After that, the P/S converting circuit 216 successively outputs the10-bit data received from the counter circuit 215 to the switchingcircuit 19 synchronously with the continuous amount sending clock Swfrom the control circuit 13.

The slider detecting circuit 22 is composed of a variable resistor 221,a capacitor 222, a comparator 223, an AND gate 224, a counter circuit225, and a P/S converting circuit 226. The variable resistor 221 isconfigured to change its resistance value in accordance with theoperational state (position) of the slider 1 cb. The variable resistor221 and the capacitor 222 compose a time constant circuit. When thecontinuous amount detection pulse Ss is inputted to the time constantcircuit, a signal whose rate of rise is changed in accordance with aresistance value of the variable resistor 221 is outputted, similarly tothe case of the pen pressure detecting circuit 21 described above. Sincethe operations of the other circuits are the same as those in the penpressure detecting circuit 21, a description thereof is omitted. It isnoted that a variable-resistance capacitor, an inductance element, orthe like may be used instead of using the variable resistor 221.

The clock generating circuit 25 generates a clock signal Sa and suppliesthe generated clock signal Sa to the control circuit 13. The controlcircuit 13 sets the timings for various kinds of operationssynchronously with the clock signal Sa. A relatively low frequency, forexample, about 8 kHz may be adopted for the clock signal Sa. The powersource 26 may be a battery, as a power source for driving the circuitsdescribed above.

[Construction of a Tablet]

Next, the construction of a tablet will be described with reference toFIG. 4. The tablet is constructed by stacking a sensor glass 206 on anupper surface of a display portion 2 b composed of a liquid crystalpanel and the like. Flexible substrates 202, 203, 204, 205 are coupledto the sensor glass 206.

The sensor glass 206 is obtained by, for example, sticking two sheets ofglasses each having a thickness of about 0.4 mm to each other. A patternof a loop coil group 30 (not shown) made from the ITO film is formed oneach of the glasses. The loop coil group 30 is composed of loop coils X1to X40 (not shown in FIG. 4) arranged in an X-axis direction, and loopcoils Y1 to Y30 (not shown in FIG. 4) arranged in a Y-axis direction,for example.

The pattern of the loop coils arranged in the X-axis direction is formedon one of the two sheets of glasses by etching, and the pattern of theloop coils arranged in the Y-axis direction is formed on the other ofthe two sheets of glasses also by etching. These glasses are made so asto sandwich a transparent insulating sheet between them, with thesurfaces of the ITO films being arranged to face each other. It is notedthat details of the disposition of the loop coils will be describedlater with reference to FIG. 5.

The flexible substrate 202 is formed, for example, with a polyimidematerial as a base, and is connected to the pattern of lines of the loopcoils X1 to X40 on the sensor glass 206. Also, folding portions forforming the loops, respectively, are disposed on the flexible substrate202. The flexible substrate 203 is formed, for example, also with apolyimide material as the base and is connected to the pattern of thelines of the loop coils X1 to X40 on the sensor glass 206. A terminalderived from the flexible substrate 203 is connected to a selectingcircuit 31, which will be described later.

Likewise, the flexible substrate 204 is formed, for example, with apolyimide material as the base and is connected to the pattern of linesof the loop coils Y1 to Y30 on the sensor glass 206. Also, foldingportions for forming the loops, respectively, are disposed on theflexible substrate 204. The flexible substrate 205 is formed, forexample, also with a polyimide material as the base and is connected tothe pattern of the lines of the loop coils Y1 to Y30 on the sensor glass206. A terminal derived from the flexible substrate 205 is connected tothe selecting circuit 31, which will be described later.

Next, an internal configuration of the tablet will be described withreference to FIG. 5. The tablet is composed of the loop coil group 30,the selecting circuit 31, a CPU 33 (control portion), a switchingcircuit 34, an amplifying circuit 35, a band-pass filter 36 (hereinafterreferred to as “a BPF 36”), a detecting circuit 37, an S/H circuit 38,an A/D converting circuit 39, a switch 40, and a signal generatingcircuit 41. As described above, the loop coil group 30 is disposed inthe form of the loop coils X1 to X40 in the X-axis direction, and theloop coils Y1 to Y30 in the Y-axis direction.

It is noted that in FIG. 5, both ends of one loop coil are representedby addition of reference symbols A and B, respectively. For example,both ends of the loop coil X1 are represented by X1A and X1B,respectively.

The size and arrangement pitch of the loop coil group 30 are determinedso that the position detection area 2 a (refer to FIG. 1) composed ofthe loop coil group 30 matches with the display area of the displayportion 2 b. Also, start points and end points of the loop coils X1 toX40 and the loop coils Y1 to Y30 composing the loop coil group 30 areconnected to the selecting circuit 31 so that corresponding ones of theloop coils can be selected. Specifically, the selecting circuit 31selects one set of terminals as a line La and a line Lb from each of theloop coils arranged in the X-axis direction and the loop coils arrangedin the Y-axis direction in accordance with a coil selection signal Spsupplied thereto from the CPU 33.

The line La and the line Lb selected by the selecting circuit 31 areboth connected to the switching circuit 34. The switching circuit 34 canconnect each of connection destinations of the line La and the line Lbeither to a transmission side (T) or to a reception side (R) inaccordance with a transmission/reception switching signal Sm suppliedthereto from the CPU 33.

When the switching circuit 34 connects each of the connectiondestinations of the line La and the line Lb to the reception side (R),the loop coil selected by the selecting circuit 31 is connected to theamplifying circuit 35 through the line La and the line Lb. Theamplifying circuit 35 amplifies the signal transmitted thereto from thecoil 12 of the position indicator.

An output terminal of the amplifying circuit 35 is connected to the BPF36, and the BPF 36 extracts only a desired frequency component from theoutput signal of the amplifying circuit 35, to thereby output thedesired frequency component thus extracted in the form of an outputsignal Sq. The output signal Sq from the BPF 36 is supplied to thedetecting circuit 37, and the detecting circuit 37 outputs a voltagecorresponding to a level of the output signal Sq from the BPF 36.

The S/H circuit 38 and the A/D converting circuit 39 periodicallyconvert a voltage of a detected signal Sr outputted from the detectingcircuit 37 into a digital value in accordance with control from the CPU33.

When the switching circuit 34 connects each of the connectiondestinations of the line La and the line Lb over to the transmissionside (T), the loop coil selected by the selecting circuit 31 isconnected to the signal generating circuit 41 through the switch 40.Thus, an AC current is caused to flow through the selected loop coilwhen the switch 40 is held in an ON state. The ON state and an OFF stateof the switch 40 are changed over to each other in accordance with atransmission control signal Sn supplied thereto from the CPU 33. The ONstate and the OFF state of the switch 40 are changed over to each othertime-sequentially to transmit a control signal to the positionindicator.

The control signal includes command information such as a commandrequesting the ID information (“100” in this embodiment), a commandrequesting the pen pressure information (“101” in this embodiment), acommand requesting the slider information (“110” in this embodiment), orthe like. It is noted that the commands are by no means limited to theseexamples, and thus when the position indicator has information otherthan the information on the pen pressure, its ID, and the slider, othercommands may be used in accordance with which these other pieces ofinformation are acquired.

[Operation of the Embodiment]

Next, an operation of this embodiment will be described. It is notedthat the description will be given below in accordance with thefollowing order.

(1) Period of Time for Coordinate Detection.

(2) Period of Time for Command Transmission.

(3) Period of Time for Timing Extraction.

(4) Period of Time for Data Reception.

(5) Initial Operation When a Position Indicator is Put down on a Tablet.

Although the actual operation is carried out in the order of (5), and(1) to (4), the description will be given below in accordance with theorder described above to render the description easy to follow andunderstand.

FIG. 6 shows an operation for detecting the pen pressure information ofthe position indicator, by transmitting the command of “101” as thecontrol signal for the position indicator. FIG. 7 shows an operation fordetecting the ID information of the position indicator by transmittingthe command of “100” as the control signal for the position indicator.FIG. 8 shows an operation for detecting the slider information of theposition indicator by transmitting the command of “110” as the controlsignal for the position indicator. In FIGS. 6 to 8, an abscissa axis ofeach of the clock signals Sa to Sr represents time, and the clocksignals Sa to Sr represent the signal waveforms in the portions in FIGS.3 and 5 designated by the same reference symbols Sa to Sr, respectively.

Note that, in FIGS. 6 to 8, the description is given on the assumptionthat the position indicator is placed in the vicinity of an intersectionpoint between the loop coil X11 and the loop coil Y8 on the sensor glass206 of the tablet, and by carrying out the initial operation which willbe described later, the CPU 33 has already recognized that the positionindicator is placed in the vicinity of the intersection point betweenthe loop coil X11 and the loop coil Y8.

(Operation when Command “101” is Transmitted)

An operation when the command of “101” for requiring to transmit the penpressure information is transmitted from the tablet to the positionindicator will be described with reference to FIG. 6.

(1) Period of Time for Coordinate Detection

The control circuit 13 of the position indicator supplies theoscillation control signal Sc to the oscillation circuit 11 so that thesignal is continuously transmitted from the coil 12 during a time periodrequired by the tablet to detect the coordinates, for example, for 1msec or more. As a result, while the oscillation control signal Sc issupplied, a coil signal Sd is generated in the coil 12, and an ACmagnetic field caused by the coil signal Sd is transmitted. Thisoperation is referred to as a continuously transmitting operation. Aperiod of time during which the position indicator carries out thecontinuously transmitting operation is a period of time during which thecoordinate detection is carried out in the tablet, and is also a periodof time during which the pen pressure information and the sliderinformation, which will be described later, are detected in the positionindicator.

For the purpose of detecting a timing at which the continuouslytransmitting operation by the position indicator is started, the CPU 33of the tablet first (previously) sends a coil selection signal Sp usedto select the loop coil X11 (or Y8) to the selecting circuit 31. Inaddition, the CPU 33 sends the transmission/reception switching signalSm, which causes the switching circuit 34 to connect each of theconnection destinations of the line La and the line Lb to the receptionside (R).

At this time, if the coil signal Sd is transmitted from the coil 12 ofthe position indicator, a voltage must be found in the detected outputSr from the detecting circuit 37 within the tablet.

The CPU 33 checks the output result from the A/D converting circuit 39,and determines that the continuously transmitting operation from theposition indicator is started when the voltage is continuously generatedin the detected output Sr for a given time period, for example, for aperiod of 128 μsec or more. This operation is carried out to distinguishsuch a continuously transmitted signal from a signal which isintermittently transmitted from the position indicator during a periodof time for data reception, which will be described later. The CPU 33subsequently carries out the coordinate detecting operation.

For the purpose of obtaining the signal levels from the five loop coilswith the loop coil X11 at the center, the CPU 33 sends a coil selectionsignal Sp so as to successively select the loop coils X9 to X13. Thecoil selection signal Sp is sent to carry out the successive selectionat every period of time, for example, of 64 μsec, for one loop coil.

At this time, a voltage corresponding to a distance between the selectedloop coil and the coil 12 of the position indicator appears in thedetected output Sr from the detecting circuit 37. In other words, avoltage distribution is obtained such that the highest voltage isobtained when the loop coil X11 closest to the position indicator isselected (Sr in FIG. 6). The X-coordinate of the position indicated bythe position indicator can be obtained from a peak level and the voltageacross the coils adjacent to each other in the voltage distribution.

Subsequently, for the purpose of obtaining the signal levels from thefive loop coils with the loop coil Y8 at the center, the CPU 33 sends acoil selection signal Sp so as to successively select the loop coils Y6to Y10. In this case as well, similarly to the case where the X-axisloop coils are selected, the successive selection is carried out atevery period of time of, for example, 64 μsec, for one loop coil. Atthis time, a voltage corresponding to a distance between the selectedloop coil and the coil 12 of the position indicator appears in thedetected output Sr from the detecting circuit 37. In other words, avoltage distribution is obtained such that the highest voltage isobtained when the loop coil Y8 closest to the position indicator isselected (Sr in FIG. 6). The Y-coordinate of the position indicated bythe position indicator can be obtained from a peak level and the voltageacross the coils adjacent to each other in the voltage distribution.

Next, for the purpose of waiting for completion of the continuouslytransmitting operation from the position indicator, the CPU 33 sends acoil selection signal Sp used to select the loop coil X11 (or Y8) to theselecting circuit 31. At this time, in the coordinate detectingoperation described above, if the peak voltage which was generated inthe loop coil (referred to as “the central coil”) has been moved to theloop coil adjacent to that loop coil, the position indicated by theposition indicator is determined to be moved, and thus the central coilthus updated is selected. Since the voltage of the detected output Sr isgradually reduced when the continuous transmission from the positionindicator has been completed, the CPU 33 determines that the continuoustransmission has been completed when the voltage of the detected outputSr becomes equal to or smaller than a given threshold Vth, and theoperation of the CPU 33 proceeds to a command transmitting operationwhich will be next described.

While the coordinate detecting operation in the tablet is carried out,that is, while the coil signal Sd is continuously transmitted from theposition indicator, the pen pressure detecting operation and the sliderdetecting operation are also carried out by the pen pressure detectingcircuit 21 and the slider detecting circuit 22 within the positionindicator, respectively. Although in this embodiment, the pen pressuredetecting operation and the slider detecting operation are carried outat the same time, hereinafter, the pen pressure detecting operation willbe described.

When the continuously transmitting operation described above is started,the control circuit 13 of the position indicator sends the continuousamount detection pulse Ss for a period of time until the oscillationoutput from the oscillation circuit 11 is sufficiently stabilized, forexample, after a lapse of 64 μsec. When the continuous amount detectionpulse Ss is inputted from the control circuit 13 to the pen pressuredetecting circuit 21, a signal St appears on the output side of the timeconstant circuit, whose rate of rise changes in accordance with the penpressure as described above. In addition, a pen pressure detectionsignal Su is outputted from the AND gate 214, whose pulse width changesin accordance with the pen pressure.

The pen pressure detection signal Su is inputted to the enable terminalEN of the counter circuit 215. Also, the number of waves of the coilsignal Sd inputted to the clock input terminal CK of the counter circuit215 is counted only during a period of time of a pulse width of the penpressure detection signal. A numerical value counted is outputted as thepen pressure information of 10 bits from the P/S converting circuit 216.

(2) Period of Time for Command Transmission

When the voltage of the detected output Sr has become equal to orsmaller than the given threshold Vth, signaling detection of thecompletion of the continuous transmission, the operation of the CPU 33of the tablet proceeds to a command transmitting operation. At thistime, the selecting circuit 31 maintains a state in which the loop coilclosest to the position indicator is kept selected.

The CPU 33 sends the transmission/reception switching signal Sm, whichcauses the switching circuit 34 to connect each of the connectiondestinations of the line La and the line Lb to the transmission side(T). In addition, the CPU 33 sends the transmission control signal Sn tothe switch 40. “1,” “0,” and “1” are successively outputted as thetransmission control signal Sn at, for example, every 128 μsec.

For a period of time during which the transmission control signal Sn isheld at “1,” the signal generating circuit 41 is connected to the loopcoil selected by the selecting circuit 31, and thus an AC current iscaused to flow through the loop coil selected by the selecting circuit31. The current caused to flow is not much because the loop coil is madefrom the ITO film, and thus the resistance value thereof is as large asseveral kilo-ohms to several tens of kilo-ohms. However, since adistance between the coil 12 of the position indicator and the loop coilis relatively short, a signal having, for example, about severalmilli-volts is generated in the coil 12 of the position indicator.

After completion of the continuously transmitting operation, the controlcircuit 13 of the position indicator outputs such a control signal Se asto hold the switch 15 in an ON state only for a period of time of threecycles of the clock signal Sa. When the signal is outputted from theloop coil of the tablet during this period of time, an amplifier outputSf appears in the output of the amplifying circuit 14, which causes anoutput Sp from the comparator 17 to become “1.”

At this time, if a period of time (128 μsec in this case) during whichthe signal of 1 bit is transmitted from the tablet is made toapproximately match the period of the clock signal Sa in the positionindicator, the signal transmitted from the tablet can be extractedsynchronously with the clock signal Sa.

In other words, if a value of the output Sg from the comparator 17 isread at a falling timing of the clock signal Sa as shown in FIG. 6, thesignal transmitted from the tablet can be extracted in the order of “1,”“0,” and “1.” When “101” is supplied as the selection signal Sk from theS/P converting circuit 18 to the switching circuit 19, the switchingcircuit 19 selects the output data from the pen pressure detectingcircuit 21 and sends the output data thus selected as the transmissiondata Sb.

In other words, in the position indicator, a period of time during whichtransmission is stopped is set after completion of the continuouslytransmitting operation, and during this period a signal from the tabletis received as a command. On the other hand, in the tablet, upondetecting the completion of the continuously transmitting operation fromthe position indicator, transmission of a command to the positionindicator is immediately started. The series of operations describedabove are one of the features of the present invention.

(3) Period of Time for Timing Extraction

When a command of 3 bits from the tablet has been detected in theposition indicator, the control circuit 13 of the position indicatorcarries out a signal transmission twice synchronously with the clocksignal Sa. Specifically, for a period of time during which the clocksignal Sa is held at “1,” the control circuit 13 carries out a controlsuch that the oscillation control signal Sc also becomes “1,” whereby asshown in FIG. 6, the intermittent signal synchronized with the clocksignal Sa is transmitted twice from the coil 12.

When the transmission of the command of 3 bits (“101” in this case) hasbeen completed on the tablet side, the CPU 33 sends thetransmission/reception switching signal Sm, which causes the switchingcircuit 34 to connect each of the connection destinations of the line Laand the line Lb to the reception side (R). As a result, the loop coilselected by the selecting circuit 31 is connected to the amplifyingcircuit 35, and thus the signal based on the two transmissions from theposition indicator described above is detected, so that the detectedoutput Sr appears as shown in FIG. 6.

At this time, in the CPU 33, a time at which the result from the A/Dconverting circuit 39 exceeds the given threshold Vth is measured twice,whereby an interval between the times of the two measurements isobtained in the form of “td.” The time td should approximately match theperiod of the clock signal Sa of the position indicator. After that, theCPU 33 can precisely extract the data transmitted thereto from theposition indicator, by detecting a signal at every td.

(4) Period of Time for Data Detection

When the two signal transmissions have been completed in the positionindicator, the pen pressure detecting circuit 21 sends the pen pressureinformation in the form of the transmission data Sb synchronously with arising of the subsequent clock signal Sa.

FIG. 6 shows an example in the case where the pen pressure informationis expressed in the form of 10 bits of “1011001010.” The transmissiondata Sb representing the pen pressure information is outputted 1 bit by1 bit synchronously with the clock signal Sa as shown in FIG. 6.

At this time, the control circuit 13 sends the coil signal Sd when thetransmission data Sb is “1,” and does not send the coil signal Sd whenthe transmission data Sb is “0.” In addition, an interval of the datasending operations approximately agrees with the time td obtained on thetablet side.

While the signal from the loop coil X11 (or Y8) is continuously detectedin the tablet, a voltage equal to or greater than the given thresholdVth is generated in the detected output Sr when the transmitted datafrom the position indicator is “1.” On the other hand, no voltage isgenerated in the detected output Sr when the transmitted data from theposition indicator is “0.”

The CPU 33 sets a point of time slightly later than the time, at whichthe detected output Sr exceeds the given threshold Vth for the secondtime during the period of time for the timing extraction describedabove, as a basing point, and checks the output result from the A/Dconverting circuit 39 at every integer multiple of the time td. Then,“1” is stored when the output from the A/D converting circuit 39 exceedsthe above given threshold Vth, while “0” is stored when the output fromthe A/D converting circuit 39 is smaller than the above given thresholdVth. By repetitively carrying out this operation 10 times, the CPU 33completes the reception of the pen pressure information of 10 bitstransmitted thereto from the position indicator. At “the point of timeslightly later than the time, at which the detected output Sr exceedsthe given threshold Vth for the second time” described above, it isassumed that a cycle (period) which is, for example, a quarter of thatof the clock signal Sa is set.

After completion of the transmission of the pen pressure information,the control circuit 13 of the position indicator starts to carry out thecontinuously transmitting operation described above again in order toallow the tablet to continuously carry out the coordinate detection.

(Operation when Command “100” is Transmitted)

FIG. 7 shows an operation when the command of “100” is transmitted fromthe tablet to the position indicator, thereby detecting the IDinformation.

FIG. 7 is different from FIG. 6 in that the data of 3 bits transmittedfrom the loop coil of the tablet during the period of time for commandtransmission is “100.” The signal is extracted in the order of “1,” “0,”and “0” in the comparator output Sg in the position indicator, and theS/P converting circuit 18 supplies the information of “100” as theselection signal Sk to the switching circuit 19. The switching circuit19 selects the signal from the ID storing memory 20 corresponding to thecommand of “100,” and supplies that signal in the form of thetransmission data Sb to the control circuit 13. FIG. 7 shows the casewhere the ID information stored in the ID storing memory 20 is expressedin the form of 10 bits of “0011100110.”

(Operation when Command “110” is Transmitted)

FIG. 8 shows an operation for transmitting the command of “110” from thetablet to the position indicator, thereby requesting the sliderinformation.

FIG. 8 is different from FIG. 6 in that the data of 3 bits transmittedfrom the loop coil of the tablet during the period of time for thecommand transmission is “110.” The signal is extracted in the order of“1,” “1,” and “0” in the comparator output Sg in the position indicator,and the S/P converting circuit 18 supplies the information of “110” asthe selection signal Sk to the switching circuit 19. The switchingcircuit 19 selects the signal from the slider detecting circuit 22corresponding to the command of “110,” and supplies the signal thusselected in the form of the transmission data Sb to the control circuit13. FIG. 8 shows the case where the slider information from the sliderdetecting circuit 22 is expressed in the form of 10 bits of“0101000101.” It is noted that although not illustrated in FIG. 8, theslider detecting circuit 22 carries out the same operation as that ofthe pen pressure detecting circuit 21 in accordance with the continuousamount detection pulses Ss to Sw as shown in FIG. 6, to thereby detectthe slider information described above.

(5) Initial Operation when a Position Indicator is Put on a Tablet.

Next, a description will be given regarding how the operation proceedsto the operations described above and shown in FIGS. 6 to 8,respectively, when the position indicator is put on the tablet from astate in which there is no position indicator on the tablet. In thisembodiment, a description will now be given with respect to a firstexample and a second example, in both of which there is no positionindicator on the tablet.

(5)-1 First Example of Initial Operation.

FIG. 9 shows the first example of an initial operation when the positionindicator is put on the tablet. In FIG. 9, an abscissa axis of each ofthe clock signals Sa to Sr represents time, and the clock signals Sa toSr represent the signal waveforms in the portions in FIGS. 3 and 5designated by the same reference symbols Sa to Sr, respectively.

In this illustrative embodiment, the position indicator alternatelyrepeats the continuously transmitting operation and the commandreceiving operation for receiving a command from the tablet, which arethe same as those previously described with reference to FIG. 6. When asignal (the received data other than “000”) is received during a periodof time for which the command receiving operation is carried out(hereinafter referred to as “a period of time for command reception”),the position indicator is determined to be placed on the tablet. Also,the position indicator transmits a signal corresponding to the outputdata from the ID storing memory 20, the pen pressure detecting circuit21, or the slider detecting circuit 22 to the tablet in accordance withthe contents of the received command.

On the other hand, when no signal (the received data of “000”) isreceived during the period of time for the command reception, theposition indicator is determined not to be placed on the tablet. Thus,the position indicator repetitively carries out the continuouslytransmitting operation.

For the purpose of detecting the signal from the position indicator, inthe tablet, the CPU 33 sends the transmission/reception switching signalSm, which causes the switching circuit 34 to connect each of theconnection destinations of the line La and the Lb to the reception side(R). In addition, the CPU 33 outputs such a coil selection signal Sp tothe selection circuit 31 as to successively select the loop coils Y1 toY30 with a period of time of, for example, 64 μsec being allocated toeach loop coil.

At this time, when the position indicator is put on the tablet, as shownin FIG. 9, the level of the detected output Sr becomes high when theloop coil is selected, which is in the vicinity of the position wherethe position indicator is put on the tablet. The CPU 33 stores thenumber (Y8 in this case) of the loop coil in which the highest voltageappears. Subsequently, the CPU 33 outputs such a coil selection signalSp as to successively select the loop coils X1 to X40 with a period oftime of, for example, 64 μsec being allocated to one loop coil. At thistime, the CPU 33 stores the number (X11 in this case) of the loop coilin which the highest voltage appears.

FIG. 9 shows that the high voltage is detected when the loop coil X11 isselected, and the detected voltages become gradually lower in the orderwhen the loop coil X12 and the loop coil X13 are successively selected.As a result, the CPU 33 can recognize that the position indicator is puton the loop coil X11.

For this reason, the CPU 33 completes the selection of the loop coil atthe loop coil X13 and outputs such a coil selection signal Sp as toselect the loop coil X11 (or Y8) in which the strongest signal isdetected. After that, the CPU 33 waits for a start of the continuouslytransmitting operation from the position indicator, and the operation ofthe CPU 33 proceeds to the operation of the coordinate detection periodas shown in FIGS. 6 to 8 at a point of time when the start of thecontinuously transmitting operation is detected.

It is noted that in FIG. 9, the CPU 33 of the tablet cannot detect asignal when the time at which the loop coil closest to the positionindicator is selected happens to fall within the period of time duringwhich the transmission from the position indicator is stopped (i.e., theperiod of time for the command reception in the position indicator).However, by determining these timings in such a way that a cycle throughwhich all of the loop coils Y1 to Y30 and the loop coils X1 to X40 areselected does not become an integer multiple of a cycle at which thecontinuously transmitting operation from the position indicator isrepetitively carried out, it can be ensured that a signal from theposition indicator is detected at least by the second round of theprocessing.

(5)-2 Second Example of Initial Operation.

FIG. 10 shows a second example of the initial operation when theposition indicator is put on the tablet. In FIG. 10, an abscissa axis ofeach of the clock signals Sa to Sr represents time, and the clocksignals Sa to Sr represent the signal waveforms in the portions in FIGS.3 and 5 designated by the same reference symbols Sa to Sr, respectively.

In this illustrative embodiment, the control signal Se is sent such thatthe position indicator does not transmit a signal and further that thecontrol circuit 13 of the position indicator turns ON the switch 15 tothereby operate the amplifying circuit 14 (hereinafter referred to as “apause state”).

The CPU 33 of the tablet outputs such a coil selection signal Sp to theselection circuit 31 as to successively select the loop coils Y1 to Y30.At this time, a time during which one loop coil is selected is madesufficiently longer than the cycle of the clock signal Sa of theposition indicator.

The CPU 33 carries out a control in such a way that for a period of timeduring which one loop coil is selected, the transmission/receptionswitching signal Sm is switched from the transmission side (T) to thereception side (R), and at the same time the transmission control signalSn is switched from ON to OFF (refer to FIG. 10). As a result, thereceiving operation is carried out following the transmitting operationwhen one loop coil is selected.

When the position indicator is put on the tablet (on the loop coil Y8 inthis case), the coil signal Sd appears in the coil 12 in the positionindicator when the loop coil near the loop coil Y8 is selected. The coilsignal Sd at this time is much weaker than the signal when theoscillation circuit 11 is operated. However, the coil signal Sd isinputted to the amplifying circuit 14 through the switch 15, and theamplifier output Sf and the comparator output Sg appear from theamplifying circuit 14 and the comparator 17, respectively, as shown inFIG. 10. In this case, the comparator output Sg rises when the loop coilY7 is selected.

The control circuit 13 of the position indicator sends a control signalSe such that the switch 15 is turned OFF as soon as the comparatoroutput Sg is detected through a path (not shown), thereby stopping theoperation of the amplifying circuit 14. Subsequently, the controlcircuit 13 of the position indicator outputs the oscillation controlsignal Sc to the oscillation circuit 11, thereby starting thecontinuously transmitting operation. By carrying out the continuouslytransmitting operation, the position indicator carries out the sameoperation as the initial operation in the first example described above,that is, the operation for repetitively carrying out the continuoustransmission. This operation is one of the features of the presentinvention.

Since the continuously transmitting operation carried out by theposition indicator is started during a period of time in which thetablet side selects the loop coil Y7, the detected output Sr from thetablet appears during this period of time as shown in FIG. 10. The CPU33 recognizes that the position indicator has been placed on the tabletby detecting the detected output Sr.

In addition, for the purpose of checking the loop coil closest to theposition indicator, the CPU 33 subsequently switches the selection ofthe loop coils one after another in the order of the loop coil Y8 andthe loop coil Y9. In this case, since the signal transmission from theposition indicator has already started, only reception needs to becarried out without transmission.

In FIG. 10, the highest voltage is detected when the loop coil Y8 isselected. However, as the CPU 33 switches the loop coil one afteranother in the order of the loop coil Y9, the loop coil Y10, and theloop coil Y11, the voltage of the detected output Sr becomes graduallylower. Therefore, the CPU 33 can recognize that the position indicatorexists on the loop coil Y8.

When the selection up to the loop coil Y11 has been completed, for thepurpose of determining of which of the loop coils in the X-axis theposition indicator is put in the vicinity, the CPU 33 successivelyselects the loop coils X1 to X40, thereby carrying out the receivingoperation.

In other words, the CPU 33 detects the highest detected output Sr whenthe loop coil X11 is selected, and as the CPU 33 subsequently switchesthe loop coils one after another in the order of the loop coil X12, andthe loop coil X13, the voltage of the detected output Sr becomesgradually lower. Therefore, the CPU 33 can recognize that the positionindicator exists on the loop coil X11. For this reason, the CPU 33completes the selection of the loop coil at the loop coil X13, andselects the loop coil X11 (or Y8) in which the strongest signal isdetected. In FIG. 10, the time at which the selection of the loop coilX13 has been completed agrees with the timing at which the continuoustransmission from the position indicator is completed. At this time,however, when the continuous transmission from the position indicator isstill continuing, the CPU 33 selects the loop coil X11 (or Y8), wherebythe detected output Sr is generated again. The CPU 33 waits for thetemporary completion of the continuous transmission from the positionindicator while looking at the voltage of the detected output Sr, andthereafter detects the timing at which the continuous transmission isstarted again. In such a manner, the operation of the CPU 33 proceeds tothe operation of the coordinate detection period in FIGS. 6 to 8.

In this illustrative example also, the CPU 33 cannot detect a signalfrom the X-axis coil when the time at which the X-axis loop coil closestto the position indicator happens to be selected during the period oftime when the transmission from the position indicator is stopped (theperiod of time for the command reception). However, by repeating theselection of all of the loop coils X1 to X40 continuously one more time,detection of the signal from the position indicator becomes possible. Inaddition, it is also possible to sufficiently lengthen a period of timeduring which the first round of the continuous transmission is carriedout when the operation of the position indicator proceeds from the pausestate to the normal operation state, to thereby allow the tablet side toselect all of the loop coils.

In this illustrative embodiment, when a command issued from the tabletis not continuously detected three times during the operations shown inFIGS. 6 to 8, respectively, it is determined that the position indicatorhas been removed from the surface of the tablet. Then, the controlcircuit 13 of the position indicator enters the pause state, that is,the operation in which no signal is transmitted while the controlcircuit 13 sends the control signal Se such that the switch 15 is turnedON to operate the amplifying circuit 14, thereby waiting to detect asignal from the tablet.

[Effects of a First Embodiment]

According to the first embodiment described above, the positionindicator enters a state in which a command signal from the tablet canbe received after completion of the continuously transmitting operation.The tablet starts to transmit a command to the position indicator afterthe timing when an end of the continuous transmission from the positionindicator is recognized in the form of reduction of the detected outputSr. In other words, the end time of the continuously transmittingoperation is shared between the position indicator and the tablet, andthe communication of a command is carried out during a short period oftime commonly recognized by both.

For this reason, a specific type of information can be selected frommultiple types of information within the position indicator andtransmitted. Accordingly, a rate of transfer of the information from theposition indicator to the tablet need not be reduced. Therefore, thesampling rate during the coordinate detection also need not be reduced.

In addition, in this embodiment, since the signal from the tablet can beamplified in the position indicator, even when the signal from thetablet is weak, the weak signal can be precisely extracted in the formof a command. Therefore, each of the loop coils of the tablet can bemade from the ITO film or the like having a high resistance value, andthe sensor glass 206 having the transparent loop coils can be disposedon the front surface of the display portion 2 b.

As a result, a command can be transmitted from a position on the sensorglass 206 to the position indicator. Thus, even when the display portion2 b becomes larger, these multiple types of information in the positionindicator, such as the specific ID information and the pen pressureinformation, can be detected by the tablet at a high speed.

In addition, according to this embodiment, the information, such as thepen pressure information and the slider information, which istransmitted from the position indicator to the tablet, is structured inthe form of digital data composed of a plurality of bits. Also, theoscillation circuit 11 is controlled in accordance with a value of thedigital data, whereby the information is transmitted in the form ofoutput/non-output of the coil signal Sd in a time-sequential manner. Forthis reason, the tablet can precisely extract the information sentthereto from the position indicator without being influenced by thenoise or the like.

In addition, according to this embodiment, before the information istransmitted from the position indicator to the tablet, the coil signalSd is transmitted twice at the timing that is synchronous with the clocksignal Sa supplied from the clock generating circuit 25. Also, after thetwo signal transmissions have been completed, the information istransmitted to the tablet 2 synchronously with the clock signal Sa. Atthe same time, in the tablet, the interval between the two transmissionsof the coil signal Sd is measured, and the digital data which issubsequently sent is detected based on the transmission interval thusmeasured. As a result, it is possible to shorten the time for thecommunication from the position indicator to the tablet, per 1 bit, andthus it is possible to realize the position detector having a highsampling rate.

In addition, according to the second example of this embodiment, sinceno signal is transmitted from the position indicator when no positionindicator is located on the tablet, it is possible to save powerconsumption in the position indicator. That is to say, the battery ofthe position indicator needs not be frequently exchanged or charged.

It is noted that although in the illustrative embodiment describedabove, an example is given in which the timing extraction period isprovided after completion of the continuously transmitting operationfrom the position indicator 1, the present invention is by no meanslimited thereto. For example, the timing extraction period may also beprovided after completion of the transmission of the 10-bit data fromthe position indicator 1 (before start of the continuously transmittingoperation from the position indicator 1), or while the data istransmitted from the position indicator 1 to the tablet (for example, ata point of time at which the transmission up to the 5 bit is completed),or during the continuously transmitting operation, or the like.

In addition, although in this embodiment, each of the loop coils in thetablet is made from the ITO film on the sensor glass 206, the presentinvention is by no means limited thereto. For example, each of the loopcoils may also be formed by printing a conductor material such as carbonon a PET film.

Also, although in this embodiment, the tablet and the display device areprovided integrally with each other, a construction may also be adoptedsuch that no display device is provided.

2. Second Embodiment

Next, a second embodiment of the present invention will be described.The second embodiment shows an example in which a rotational angle ofthe position indicator can be obtained relative to a rotational axisformed by a direction vertical to the tablet surface. The assignee ofthe present application has previously disclosed one such positiondetector in Japanese Patent Laid-Open No. H8-30374 (corresponding toU.S. Pat. No. 5,644,108, which is explicitly incorporated by referenceherein). This embodiment shows an example in which the rotational angleof the position indicator can be obtained, even on the tablet surfacethat includes loop coils each made from an ITO film or the like having ahigh resistance value. In this embodiment, the tablet has the sameconstruction and configuration as those shown in FIGS. 4 and 5,respectively, and used in the first embodiment.

[Construction of a Position Indicator]

FIG. 11 is a partial cross sectional view showing a construction of theposition indicating portion of the position indicator in thisembodiment. As shown in FIG. 11, two magnetic material cores 51 and 52are provided in the position indicating portion. Although a ferritematerial is desirable as the material used in each of the magneticmaterial cores 51 and 52, any other suitable material may also be used.In addition, a construction with no core may also be adopted.

A coil 53 (second coil) and a coil 54 (first coil) are wound around themagnetic material core 51. The coil 53 is wound only around the magneticmaterial core 51, while the coil 54 is wound around the magneticmaterial core 51 and the magnetic material core 52 so as to bundle thetwo cores 51 and 52 together. This construction is the same as thatdisclosed in Japanese Patent Laid-Open No. H8-30374.

[Internal Configuration of a Position Indicator]

FIG. 12 is a diagram showing an internal configuration of the positionindicator according to this embodiment. In FIG. 12, the same constituentportions as those in FIGS. 3 and 11 are designated by the same referencenumerals, respectively. The position indicator is provided with theoscillation circuit 11, the coil 53, the coil 54, the control circuit13, the amplifying circuit 14, the switch 15, the detecting circuit 16,the comparator 17, the S/P converting circuit 18, the switching circuit19, the ID storing memory 20, the pen pressure detecting circuit 21, theclock generating circuit 25, and the power source 26.

The oscillation circuit 11 is a circuit which is operated together withthe coil 54 in accordance with an oscillation control signal Sc suppliedthereto from the control circuit 13, thereby generating a coil signal Sdhaving a predetermined frequency in the coil 54. The coil 54 generatesan AC magnetic field in accordance with the coil signal Sd. The tabletdetects the AC magnetic field generated from the coil 54 in the positionindicator, thereby obtaining the information on the coordinatesindicated by the position indicator, the pen pressure, and the like.

Both ends of the coil 53 are connected to opposite terminals of a switch55, respectively, and the switch 55 is controlled so as to be heldeither in an ON state or in an OFF state in accordance with a secondcoil control signal Sj supplied thereto from the control circuit 13.

Since both ends of the coil 53 are opened when the switch 55 is held inthe OFF state, the coil 53 exerts no influence on the magnetic fieldgenerated from the coil 54. Therefore, the coordinates of a middleposition between the magnetic material core 51 and the magnetic materialcore 52 is detected in the tablet.

Both ends of the coil 53 are short-circuited when the switch 55 is heldin the ON state. An electromotive force is generated in theshort-circuited coil 53 in such a direction as to cancel a change inmagnetic flux passing through the magnetic material core 51. For thisreason, less AC magnetic field passes through the magnetic material core51 and, thus, the magnetic flux passing through the coil 54 isconcentrated only on the magnetic material core 52. Therefore, thecoordinates corresponding to the magnetic material core 52 are detectedin the tablet.

Therefore, the rotational angle of the position indicator, with thedirection vertical to the tablet surface as the axis, can be obtainedfrom the coordinate values detected in the tablet when the switch 55 isheld in the OFF state, and the coordinate values detected in the tabletwhen the switch 55 is held in the ON state.

Since other configurations are the same as those in FIG. 3, adescription thereof is omitted here.

[Operation of the Embodiment]

Next, an operation in this embodiment will be described with referenceto FIG. 13. FIG. 13 shows a situation of the operation for transmittingthe command of “110” from the tablet 2 to the position indicator,thereby detecting the rotational angle with the direction vertical tothe tablet surface of the position indicator as the axis. In FIG. 13, anabscissa axis of each of the clock signals Sa to Sr represents time, andthe clock signals Sa to Sr represent the signal waveforms in theportions in FIGS. 5 and 12 designated by the same reference symbols Sato Sr, respectively.

The CPU 33 of the tablet is assumed to find out in this embodiment aswell that the position indicator is placed in the vicinity of theintersection point between the loop coil X11 and the loop coil Y8 bycarrying out the initial operation, and thus an operation after thatoperation will now be described. It is noted that in this embodiment,the commands as the control signals issued from the tablet are expressedin the form of “101” and “100,” respectively, and are the same as thosein the first embodiment, and thus the same operations as those describedwith reference to FIGS. 6 and 7, respectively, are carried out. Inaddition, the initial operations when the position indicator is put onthe tablet from the state in which no position indicator exists on thetablet are also the same as those described with reference to FIGS. 9and 10, respectively.

In FIG. 13, the control circuit 13 of the position indicator suppliesthe oscillation control signal Sc to the oscillator circuit 11 so thatthe signal is continuously transmitted from the coil 54 during a timerequired for the tablet to detect the coordinates, for example, for 1msec or more. As a result, the position indicator carries out thecontinuously transmitting operation.

For the purpose of detecting the timing at which the continuouslytransmitting operation from the position indicator is started, the CPU33 of the tablet first (previously) sends the coil selection signal Spused to select the loop coil X11 (or Y8) to the selecting circuit 31. Inaddition, the CPU 33 sends the transmission/reception switching signalSm, which causes the switching circuit 34 to connect each of theconnection destinations of the line La and the line Lb to the receptionside (R).

The CPU 33 checks the output result from the A/D converting circuit 39,and determines that the continuously transmitting operation from theposition indicator is started when the voltage is continuously generatedin the detected output Sr for the given time, for example, for theperiod of time of 128 μsec or more. Subsequently, the CPU 33 carries outthe same coordinate detecting operations as those in the cases of FIGS.6 and 7.

In other words, for the purpose of obtaining the signal levels from thefive loop coils with the loop coil X11 at the center, the CPU 33 sendsthe coil selection signal Sp so as to successively select the loop coilsX9 to X13. The coil selection signal Sp is sent so as to carry out thesuccessive selection at every period of time of, for example, 64 μsec,for one loop coil. Subsequently, for the purpose of obtaining the signallevels from the five loop coils with the loop coil Y8 at the center, theCPU 33 sends the coil selection signal Sp so as to successively selectthe loop coils Y6 to Y10.

At this time, the voltage corresponding to the distance between theselected loop coil and the coil 54 of the position indicator appears inthe detected output Sr from the detecting circuit 37. In other words, avoltage distribution is obtained such that the highest voltage isobtained when the loop coil X11 and the loop coil Y8 each closest to theposition indicator are selected. The X-coordinate value and theY-coordinate value of the position indicated by the position indicatorcan be obtained from a peak level and the voltage across the coilsadjacent to each other in the voltage distribution. The coordinatevalues obtained at this time represent an intermediate position betweenthe magnetic material core 51 and the magnetic material core 52. In thefollowing description, these coordinates is referred to as “firstcoordinates.”

Next, for the purpose of waiting for the completion of the continuouslytransmitting operation from the position indicator, the CPU 33 sends thecoil selection signal Sp used to select the loop coil X11 (or Y8) to theselecting circuit 31. At this time, in the coordinate detectingoperation described above, if the peak voltage which was generated inthe loop coil has been moved to the loop coil adjacent to that loopcoil, the position indicated by the position indicator is determined tobe moved, and thus the central coil thus updated is selected. Since thevoltage of the detected output Sr is gradually reduced when thecontinuous transmission from the position indicator has been completed,the CPU 33 determines that the continuous transmission has beencompleted at a point of time when the voltage of the detected output Srbecomes equal to or smaller than the given threshold Vth, and theoperation of the CPU 33 proceeds to the command transmitting operation.

The transmission of commands from the tablet to the position indicatorare carried out in the same manner as those in the cases of FIGS. 6 and7, respectively. In other words, when the loop coil (X11 in this case)closest to the position indicator is kept selected, the CPU 33 sends thetransmission/reception switching signal Sm, which causes the switchingcircuit 34 to connect each of the connection destinations of the line Laand the Line Lb to the transmission side (T). In addition, the CPU 33sends the transmission control signal Sn to the switch 40. “1,” “1,” and“0” are successively outputted as the transmission control signal Sn at,for example, every 128 μsec. For the period of time during which thetransmission control signal Sn is held at “1,” the AC current is causedto flow through the loop coil selected by the selecting circuit 31.

After completion of the continuously transmitting operation, the controlcircuit 13 of the position indicator outputs such a control signal Se asto hold the switch 15 in an ON state only for a period of time of threecycles of the clock signal Sa. When the signal is outputted from theloop coil of the tablet during this period of time, an amplifier outputSf appears in the output of the amplifying circuit 14, which causes theoutput Sg from the comparator 17 to become “1.”

At this time, if a period of time (128 μsec in this case) during whichthe signal of 1 bit is transmitted from the tablet is made toapproximately match the period (cycle) of the clock signal Sa in theposition indicator, the signal transmitted from the tablet can beextracted synchronously with the clock signal Sa. In other words, if thevalue of the output Sg from the comparator 17 is read at the fallingtiming of the clock signal Sa as shown in FIG. 13, the signaltransmitted from the tablet can be extracted in the order of “1,” “1,”and “0.” The operations so far are carried out in the same manner asthose in the cases of FIGS. 6 and 7, respectively.

When the control circuit 13 of the position indicator has recognizedthat a command issued from the tablet is “110,” which requests theoperation for detection of the rotational angle, the control circuit 13sends such a second coil control signal Sj as to turn ON the switch 55.As a result, the coil 53 is short-circuited.

The control circuit 13 supplies the oscillation control signal Sc to theoscillation circuit 11 in such a way that for the time required for thetable to detect the coordinates, for example, 1 msec or more, the signalis continuously transmitted from the coil 54. As a result, the positionindicator carries out the continuously transmitting operation. At thistime, since the coil 53 is short-circuited by the switch 55, themagnetic field generated due to the AC current caused to flow throughthe coil 54 hardly passes through the magnetic material core 51, andthus is concentrated on the magnetic material core 52.

On the other hand, in the tablet, similarly to the case of the firstcoordinate detecting operation described above, the signal levels aresuccessively detected from the five loop coils with the loop coil X11 atthe center, and the five loop coils with the loop coil Y8 at the center.As a result, a coordinate position (hereinafter referred to as “secondcoordinates”) corresponding to the magnetic material core 52 isobtained.

The CPU 33 can obtain the rotational angle of the position indicator,with the direction vertical to the tablet surface as the axis, fromthese two coordinate values (the first coordinates and the secondcoordinates). In other words, a change in the magnetic flux distributionpassing through the coil, caused by the transmission of the controlsignal to the position indicator, is detected either in the form of achange in signal strength or in the form of a change in coordinateposition.

Although in this embodiment, the operation for detection of therotational angle is carried out when the command issued from the tabletis “110,” any other suitable command may also be assigned.

[Effects of a Second Embodiment]

According to this embodiment, in addition to the effects of the firstembodiment described above, the following effects are obtained. Since inthe second embodiment, the communication of the command from the tabletto the position indicator can be carried out during a short time, it ispossible to realize the position detector which can detect therotational angle of the position indicator at a high sampling raterelative to the direction vertical to the tablet surface as the axis.

In addition, in this embodiment as well, since the signal from thetablet can be amplified in the position indicator, even when the signalfrom the tablet is weak, the weak signal can be precisely extracted inthe form of a command. Therefore, each of the loop coils of the tabletcan be made from a ITO film or the like having a high resistance value,and the sensor glass 206 having such transparent loop coils can bedisposed on the front surface of the display portion 2 b.

3. Third Embodiment

Next, a third embodiment of the present invention will be described.This embodiment is such that two position indicating portions (the pentip side and the eraser side) are provided in the position indicator,and it is possible to detect which side of the position indicator isdirected to the tablet surface.

The position indicator of this embodiment does not have multiple typesof information, unlike each of the first embodiment and the secondembodiment, and has only the pen pressure information either on the pentip side or on the eraser side.

[Construction of a Position Indicator]

FIG. 14 is a partial cross sectional view showing a construction of theposition indicator according to this embodiment. The position indicatorof this embodiment also has the pen-like shape, and the tip portion ofthe rod 1 b protrudes from the main body 1 a. The position indicator isused in such a way that the tip portion of the rod 1 b contacts thetablet surface. Reference numeral 62 designates a hollow-shaped coil.The rod 1 b extends completely through the coil 62. In addition, avariable-capacitance capacitor 73 is disposed on a side of the rod 1 bopposite to the tip portion of the rod 1 b.

The variable-capacitance capacitor 73 changes its capacitance inaccordance with a magnitude of the pen pressure applied to the rod 1 b.A load applied to the variable-capacitance capacitor 73 is detected inthe form of the pen pressure information by a pen pressure detectingcircuit 64, which will be described later.

An eraser side is provided in the other end of the position indicatoropposite to the pen side. On the eraser side, an eraser rod 1 eprotrudes from the main body 1 a. The position indicator is used in sucha way that a tip portion of the eraser rod 1 e contacts the tabletsurface. Reference numeral 79 designates a hollow-shaped coil and theeraser rod 1 e extends completely through the coil 79. In addition, avariable-capacitance capacitor 75 is disposed on the side of the eraserrod 1 e opposite to the tip portion of the eraser core 1 e. Thevariable-capacitance capacitor 75 changes its capacitance in accordancewith the magnitude of the pen pressure applied to the eraser core 1 e.The load applied to the variable-capacitance capacitor 75 is detected inthe form of the pen pressure information by a pen pressure detectingcircuit 76, which will be described later. In addition, a power source78 is provided in a central portion of the position indicator.

[Internal Configuration of a Position Indicator]

FIG. 15 is a diagram showing an internal configuration of the positionindicator according to this embodiment. Portions composing the positionindicator include portions relating to an operation of the pen tip side,and portions relating to an operation of the eraser side. Also, theseblocks are controlled by a control circuit 56.

The portions relating to the operation of the pen tip side include anoscillation circuit 61, the coil 62, an amplifying circuit 65, a switch66, a detecting circuit 67, a comparator 68, the variable-capacitancecapacitor 73, and the pen pressure detecting circuit 64. The portionsrelating to the operation of the eraser side include an oscillationcircuit 63, the coil 79, an amplifying circuit 69, a switch 70, adetecting circuit 71, a comparator 72, a variable-capacitance capacitor75, and a pen pressure detecting circuit 76.

The oscillation circuit 61 on the pen tip side is a circuit which isoperated together with the coil 62 in accordance with an oscillationcontrol signal Sc1 supplied thereto from the control circuit 56, tothereby generate a coil signal Sd1 having a predetermined frequency inthe coil 62. The tablet detects an AC magnetic field generated from thecoil 62 of the position indicator, to thereby obtain the informationregarding the coordinates indicated by the pen tip side of the positionindicator on the tablet, the pen pressure, and the like.

The amplifying circuit 65 is connected to the coil 62 through the switch66, and amplifies the signal induced in the coil 62 by the tablet. Thedetecting circuit 67 outputs a voltage corresponding to a level of theoutput signal from the amplifying circuit 65. The comparator 68 detectswhether or not the output voltage from the detecting circuit 67 is equalto or larger than a given voltage, and outputs a detection result as adigital signal. These configurations are adopted for the purpose ofdetecting whether or not a signal appears in the coil 62 during thepause period of the oscillation circuit 61, to thereby detect whether ornot the pen tip side of the position indicator exists on the tablet.

The oscillation circuit 63 on the eraser side is a circuit which isoperated together with the coil 79 in accordance with an oscillationcontrol signal Sc2 supplied thereto from the control circuit 56, tothereby generate a coil signal Sd2 having a predetermined frequency inthe coil 79. The tablet detects an AC magnetic field generated from thecoil 79 of the position indicator, to thereby obtain the informationregarding the coordinates indicated by the eraser side of the positionindicator, the pen pressure, and the like.

The amplifying circuit 69 on the eraser side is connected to the coil 79through the switch 70, and amplifies the signal induced in the coil 79by the tablet. The detecting circuit 71 outputs a voltage correspondingto a level of the output signal from the amplifying circuit 69. Thecomparator 72 detects whether or not the output voltage from thedetecting circuit 71 is equal to or larger than a given voltage, andoutputs a detection result as a digital signal. These configurations areadopted for the purpose of detecting whether or not a signal appears inthe coil 79 during the pause period of the oscillation circuit 63, tothereby detect whether or not the eraser side of the position indicatorexists on the tablet.

The variable-capacitance capacitor 73 on the pen tip side is a capacitorwhich changes its capacitance in accordance with the pen pressureapplied to the pen tip side. The pen pressure detecting circuit 64converts the capacitance value of the variable-capacitance capacitor 73into a digital value, and supplies the resulting digital value as thepen pressure information Sb1 on the pen tip side to the control circuit56. Likewise, the pen pressure detecting circuit 76 converts thecapacitance value of the variable-capacitance capacitor 75 into adigital value, and supplies the resulting digital value as the penpressure information Sb2 on the eraser side to the control circuit 56.Each of the pen pressure detecting circuit 64 and the pen pressuredetecting circuit 76 has the same configuration as that of the penpressure detecting circuit 21 described in the first embodiment.

The clock generating circuit 25 generates a clock signal Sa to supplythe clock signal Sa thus generated to the control circuit 56. Thecontrol circuit 56 sets (creates) timings for various kinds ofoperations synchronously with the clock signal Sa. A relatively lowfrequency, for example, about 8 kHz is adopted for the clock signal Sa.The power source 78 may be a battery for driving the circuits describedabove.

[Configuration of a Tablet]

FIG. 16 is a diagram showing an example of an internal configuration ofthe tablet of this embodiment. In FIG. 16, portions having the sameconfigurations as those in the portions in FIG. 5 are designated by thesame reference numerals, respectively, and thus a detailed descriptionthereof is omitted. The tablet shown in FIG. 16 is also composed of theloop coil group 30, the selecting circuit 31, the CPU 33, the switchingcircuit 34, the amplifying circuit 35, the BPF 36, the detecting circuit37, the S/H circuit 38, the A/D converting circuit 39, and the signalgenerating circuit 41. The switch 40 in the first embodiment is notprovided in the tablet in this embodiment. The reason for this isbecause the information that the position indicator transmits to thetablet is only the pen pressure information either on the pen tip sideor on the eraser side, and thus no command needs to be transmitted fromthe tablet to the position indicator.

[Operation of the Embodiment]

Next, an operation in this embodiment will be described in accordancewith the following order.

(1) An initial operation when the pen tip side is placed on the tablet.

(2) An operation for detecting the coordinates and the pen pressure whenthe pen tip side is placed on the tablet.

(3) An initial operation when the eraser side is placed on the tablet.

(4) An operation for detecting the coordinates and the pen pressure whenthe eraser side is placed on the tablet.

(1) an Initial Operation when the Pen Tip Side is Placed on the Tablet.

In this embodiment, when the position indicator does not exist on thetablet (initial state), the position indicator transmits the signal fromneither of the coil 62 and the coil 79. At this time, by turning ON boththe switch 66 and the switch 70, the control circuit 56 of the positionindicator can receive a signal from the tablet on either of the pen tipside and the eraser side.

FIG. 17 is a timing chart showing the initial operation when the pen tipside of the position indicator is put on the tablet. In FIG. 17, anabscissa axis of each of the clock signals Sa to Sr represents time, andthe clock signals Sa to Sr represent the signal waveforms in theportions in FIGS. 15 and 16 designated by the same reference symbols Sato Sr, respectively.

The CPU 33 of the tablet outputs a coil selection signal Sp such thatthe loop coils Y1 to Y30 are successively selected to the selectingcircuit 31. At this time, a time during which one loop coil is selectedis set as being sufficiently longer than the cycle of the clock signalSa of the position indicator.

The CPU 33 changes the transmission/reception switching signal Sm fromthe transmission side (T) to the reception side (R) during the period oftime when one loop coil is selected. As a result, when one loop coil isselected, the receiving operation is carried out following thetransmitting operation.

When the pen tip side of the position indicator is placed on the tablet(on the loop coil Y8 in this case), the coil signal Sd1 appears in thecoil 62 of the pen tip side of the position indicator when the loop coilnear the loop coil Y8 is selected. The coil signal Sd1 at this time ismuch weaker than the signal when the oscillation circuit 61 is operated.However, when the coil signal Sd1 is inputted to the amplifying circuit65 through the switch 66, the amplifier output Sf1 and the comparatoroutput Sg1 appear from the amplifying circuit 65 and the comparator 68,respectively, as shown in FIG. 17. In this case, the comparator outputSg1 rises when the loop coil Y7 is selected.

The control circuit 56 of the position indicator sends the controlsignal Se1 such that the switch 66 is turned OFF as soon as thecomparator output Sg1 is detected, to thereby stop the operation of theamplifying circuit 65. Concurrently with this operation, the controlcircuit 56 sends such a control signal Se2 as to turn OFF the switch 70,to thereby stop the operation of the amplifying circuit 69.Subsequently, the control circuit 56 outputs an oscillation controlsignal Sc1 to the oscillation circuit 61, to thereby start thecontinuously transmitting operation from the pen tip side. Thisoperation is one of the features of the present invention.

Since the continuously transmitting operation carried out by theposition indicator is started during a period of time when the tabletside selects the loop coil Y7, the detected output Sr from the tabletappears during this period of time as shown in FIG. 17. The CPU 33recognizes that the position indicator has been placed on the tablet bydetecting the detected output Sr.

In addition, for the purpose of checking the loop coil closest to theposition indicator 1, the CPU 33 subsequently switches the selection ofthe loop coil one after another in the order of the loop coil Y8 and theloop coil Y9. In this case, since the signal transmission from theposition indicator is already started, transmission need not be carriedout and only reception has to be carried out.

In FIG. 17, the highest voltage is detected when the loop coil Y8 isselected. However, as the CPU 33 switches the loop coil one afteranother in the order of the loop coil Y9, the loop coil Y10, the loopcoil Y11, and the loop coil 12, the voltage of the detected output Srbecomes gradually lower. Therefore, the CPU 33 can recognize that theposition indicator exists on the loop coil Y8.

When the selection up to the loop coil Y12 has been completed, for thepurpose of determining of which of the loop coils in the X-axis theposition indicator is put in the vicinity, the CPU 33 successivelyselects the loop coils X1 to X40, to thereby carry out the receivingoperation. In other words, the CPU 33 detects the highest detectedoutput Sr when the loop coil X11 is selected, and as the CPU 33 switchesthe loop coil one after another in the order of the loop coil X12, theloop coil X13, and the loop coil X14, the voltage of the detected outputSr becomes gradually lower. Therefore, the CPU 33 can recognize that theposition indicator exists on the loop coil X11. Therefore, the CPU 33completes the selection of the loop coils at the loop coil X14, andselects the loop coil X11 (or Y8) in which the strongest signal isdetected. The CPU 33 selects the loop coil X11 (or Y8), whereby thedetected output Sr is generated again. The CPU 33 waits for thetemporary completion of the continuous transmission from the positionindicator while looking at the voltage of the detected output Sr, andthereafter detects the timing at which the continuous transmission isstarted again. In such a manner, the operation of the CPU 33 proceeds tothe operation for detecting the coordinates and the pen pressure, whichwill be described later.

(2) an Operation for Detecting the Coordinates and the Pen Pressure whenthe Pen Tip Side is Placed on the Tablet.

FIG. 18 shows that an operation for detecting the coordinates and thepen pressure is repetitively carried out after it has been determinedthat the position indicator exists in the vicinity of an intersectionpoint between the loop coil X11 and the loop coil Y8 through the initialoperation described above.

For the purpose of detecting a timing at which the continuouslytransmitting operation from the position indicator is started, the CPU33 of the tablet sends a coil selection signal Sp used to select theloop coil X11 (or Y8) to the selecting circuit 31. In addition, the CPU33 sends the transmission/reception switching signal Sm, which causesthe switching circuit 34 to connect each of the connection destinationsof the line La and the line Lb to the reception side (R).

The CPU 33 checks the output result from the A/D converting circuit 39,and determines that the continuously transmitting operation from theposition indicator is started when the voltage is continuously generatedin the detected output Sr for a given time, for example, for a period oftime of 128 μsec or more. This operation is carried out to distinguish acontinuous signal from a signal which is intermittently transmitted fromthe position indicator, similarly to the case of the first embodiment.The CPU 33 subsequently carries out the coordinate detecting operation.

The coordinate detecting operation is carried out in the same manner asthat described with reference to FIGS. 6 to 8 in the first embodiment,and thus the X-coordinate and the Y-coordinate of the position indicatorare obtained.

Next, for the purpose of waiting for completion of the continuouslytransmitting operation from the position indicator, the CPU 33 sends thecoil selection signal Sp used to select the loop coil X11 (or Y8) to theselecting circuit 31. At this time, in the coordinate detectingoperation described above, if the peak voltage which was generated inthe loop coil has been moved to the loop coil adjacent to that loopcoil, the position indicated by the position indicator is determined tobe moved, and thus the central coil thus updated is selected. Since thevoltage of the detected output Sr is gradually reduced when thecontinuous transmission from the position indicator has been completed,the CPU 33 determines that the continuous transmission has beencompleted at a point of time when the voltage of the detected output Srbecomes equal to or smaller than the given threshold Vth, and theoperation of the CPU 33 proceeds to a tablet signal transmissionoperation for a period of time, which will be next described.

Note that, while the coordinate detecting operation in the tablet iscarried out, that is, while the continuous transmission from theposition indicator is carried out, the pen pressure detecting operationis carried out by the pen pressure detecting circuit 64 within theposition indicator similarly to the case of the first embodiment. Bycarrying out the initial operation described above, the control circuit56 of the position indicator has recognized that the pen tip side wasplaced on the tablet. Therefore, the control circuit 56 carries out acontrol in such a way that the pen pressure detecting circuit 64 isoperated through the path (not shown), while the pen pressure detectingcircuit 76 (on the eraser side) is not operated.

When the voltage of the detected output Sr has become equal to orsmaller than the given threshold Vth, to indicate the completion of thecontinuous transmission, the operation of the CPU 33 of the tabletproceeds to a tablet signal transmission operation for a period of time.The selecting circuit 31 sends the transmission/reception switchingsignal Sm, which causes the switching circuit 34 to connect each of theconnection destinations of the line La and the line Lb to thetransmission side (T), for example, for a period of time of 128 μsec,while the loop coil closest to the position indicator is kept selected.As a result, the loop coil thus selected is connected to the signalgenerating circuit 41, so that an AC current is caused to flow throughthat loop coil. The current caused to flow is not much because the loopcoil is made from an ITO film and the like, and thus the resistancevalue thereof is as large as several kilo-ohms to several tens ofkilo-ohms. However, a signal having, for example, about severalmilli-volts is generated in the coil 62 of the pen tip side of theposition indicator.

After completion of the continuously transmitting operation, for thepurpose of receiving the signal from the tablet, the control circuit 56of the position indicator outputs such a control signal Se1 as to holdthe switch 66 in an ON state only for a period of time of two cycles ofthe clock signal Sa. When the signal is outputted from the loop coil ofthe tablet during this period of time, an amplifier output Sf1 appearsin the output of the amplifying circuit 65, which causes an output Sg1from the comparator 68 to become “1.” As a result, the control circuit56 recognizes that the position indicator is continuously placed on thetablet.

Having detected the output Sg1 from the comparator 68 during the tabletsignal transmission period described above, the control circuit 56 ofthe position indicator proceeds to carry out the same operation fortiming extraction as that in the first embodiment. In other words, thecontrol circuit 56 of the position indicator transmits the signal twicefrom the coil 62 of the pen tip side synchronously with the clock signalSa.

Note that, when no output Sg1 from the comparator 68 is detected duringthe tablet signal transmission period described above, the controlcircuit 56 of the position indicator determines that the positionindicator has been removed from a position on the tablet, and controlsthe signals so as to obtain the initial operation state described above.

When the transmission of the signal from the loop coil has beencompleted, the operation on the tablet side proceeds to the timingextraction period. The CPU 33 measures twice a time at which the resultfrom the A/D converting circuit 39 exceeds the given threshold Vth,similarly to the case of the first embodiment. Thus, an interval betweenthe times of the two measurements is obtained in the form of “td.” Thetime td should approximately match the cycle of the clock signal Sa ofthe position indicator. After that, the CPU 33 can precisely extract thedata transmitted thereto from the position indicator by detecting thesignal at every time period of td.

When the two transmissions described above have been completed in theposition indicator, the control circuit 56 successively sends data of 11bits, which will be described later, as an oscillation control signalSc1 to the oscillation circuit 61 on the pen tip side. The data of 11bits is outputted synchronously with the rising of the clock signal Sa.Thus, the oscillation control signal Sc1 is outputted as “1” when thedata is “1,” and the oscillation control signal Sc1 is outputted as “0”when the data is “0.” The first bit of the data of 11 bits representsthe direction of the position indicator oriented (pointed) to the tabletsurface, and is “0” representing the pen tip side in the example of FIG.18. In addition, in this embodiment, there is shown a case where the penpressure information on the pen pressure side is “1011001010.”

While the signal from the loop coil X11 (or Y8) is continuously detectedin the tablet, a voltage equal to or larger than the given threshold Vthis generated in the detected output Sr when the transmitted data fromthe position indicator is “1.” On the other hand, no voltage isgenerated in the detected output Sr when the transmitted data from theposition indicator is “0.”

The CPU 33 sets a point of time slightly later than the time, at whichthe detected output Sr exceeds the given threshold Vth for the secondtime during the period of time for the timing extraction describedabove, as a basing point, and checks the output result from the A/Dconverting circuit 39 at every integer multiple of the time td. Then,“1” is stored when the output from the A/D converting circuit 39 exceedsthe above given threshold Vth, and “0” is stored when the output fromthe A/D converting circuit 39 is smaller than the above given thresholdVth. By repetitively carrying out this operation 11 times, the CPU 33completes the reception of the pen pressure information of 11 bitstransmitted thereto from the position indicator. In FIG. 18, since thefirst data sent from the position indicator is “0,” the CPU 33 canrecognize that the pen tip side is oriented (pointed) to the tablet.This operation is one of the features of the present invention.

After completion of the transmission of the pen pressure information,the control circuit 56 of the position indicator starts to carry out thecontinuously transmitting operation described above again in order tocontinuously carry out the coordinate detection in the tablet.

(3) an Initial Operation when the Eraser Side is Placed on the Tablet.

FIG. 19 is a timing chart showing an initial operation when the eraserside of the position indicator is placed on the tablet. In FIG. 19, anabscissa axis of each of the clock signals Sa to Sr represents time, andthe clock signals Sa to Sr represent the signal waveforms in theportions in FIGS. 15 and 16 designated by the same reference symbols Sato Sr, respectively. The initial operation when the eraser side isplaced on the tablet is carried out completely in the same manner asthat in the case of the pen tip side.

The CPU 33 of the tablet successively selects the loop coils Y1 to Y30for the selecting circuit 31 through switching, and continuously carriesout the transmission and the reception while one loop coil is selected.

When the eraser side of the position indicator is placed on the tablet(on the loop coil Y17 in this case), the coil signal Sd2 appears in thecoil 79 of the eraser side of the position indicator when the loop coilnear the loop coil Y17 is selected. The coil signal Sd2 at this time ismuch weaker than the signal when the oscillation circuit 63 is operated.However, when the coil signal Sd2 is inputted to the amplifying circuit69 through the switch 70, the amplifier output Sf2 and the comparatoroutput Sg2 appear from the amplifying circuit 69 and the comparator 72,respectively, as shown in FIG. 19. In this case, the comparator outputSg2 rises when the loop coil Y16 is selected.

The control circuit 56 of the position indicator sends the controlsignal Se2 such that the switch 70 is turned OFF as soon as thecomparator output Sg2 is detected, to thereby stop the operation of theamplifying circuit 69. Concurrently with this operation, the controlcircuit 56 sends such a control signal Se1 as to turn OFF the switch 66,to thereby stop the operation of the amplifying circuit 65.Subsequently, the control circuit 56 outputs an oscillation controlsignal Sc2 to the oscillation circuit 63, to thereby start the operationfor the continuous transmission from the eraser side.

Since the continuously transmitting operation carried out by theposition indicator is started during a period of time when the tabletside selects the loop coil Y16, the detected output Sr from the tabletappears during this period of time as shown in FIG. 19. The CPU 33recognizes that the position indicator has been placed on the tablet bydetecting the detected output Sr. After that, the CPU 33 of the tabletobtains an approximate position on the tablet on which the positionindicator is placed, similarly to the case described with reference toFIG. 17. The case where the eraser side of the position indicator isplaced in the vicinity of the intersection point between the loop coilX22 and the loop coil Y17 is shown in this embodiment.

Subsequently, the CPU 33 selects the loop coil X22 (or Y17) in which thestrongest signal is detected. When the CPU 33 selects the loop coil X22(or Y17), the detected output Sr is generated again. The CPU 33 waitsfor the temporary completion of the continuous transmission from theposition indicator while looking at the voltage of the detected outputSr, and thereafter detects the timing at which the continuoustransmission is started again. In such a manner, the operation of theCPU 33 proceeds to the operation for detecting the coordinates and thepen pressure, which will be described later.

(4) an Operation for Detecting the Coordinates and the Pen Pressure whenthe Eraser Side is Placed on the Tablet.

FIG. 20 shows that an operation for detecting the coordinates and thepen pressure is repetitively carried out after it has been determinedthat the position indicator exists in the vicinity of the intersectionpoint between the loop coil X22 and the loop coil Y17 through theinitial operation described above. This operation is carried outcompletely in the same manner as that in the pen tip side operationdescribed with reference to FIG. 18.

FIG. 20 is different from FIG. 18 only in the content of the data of 11bits transmitted from the position indicator. In FIG. 20, since thefirst data of the data of 11 bits detected on the tablet side is “1,”the CPU 33 can recognize that the eraser side is oriented to the tablet.FIG. 20 shows a case where the pen pressure information on the eraserside is “1101000101.”

[Effects of a Third Embodiment]

According to this embodiment, since no signal is transmitted from theposition indicator when no position indicator exists on the tablet, itis possible to save the power consumption in the position indicator. Inother words, the battery of the position indicator needs not to beexchanged or charged frequently.

In addition, according to this embodiment, the direction of the positionindicator oriented to the tablet is determined based on the direction(or the side) through which the signal from the tablet is inputted, andthe position indication signal is transmitted only from the sideoriented to the tablet. Therefore, even when a plurality of positionindicating portions are provided in the position indicator, the powerconsumption of the position indicator does not substantially increase.Thus, the battery of the position indicator needs not to be exchanged orcharged frequently.

In addition, in this embodiment as well, since the signal from thetablet is amplified in the position indicator, the signal can betransmitted to the position indicator by the sensor glass disposed onthe front surface of the display device. Therefore, with thelarge-scaled display device, it is possible to detect the orientingdirection indicated by the position indicator, which is provided with aplurality of position indicating portions (e.g., the pen tip side andthe eraser side).

In this embodiment, the amplifying circuit, the detecting circuit, andthe comparator are provided in each of the pen tip side and the eraserside. However, the amplifying circuit, the detecting circuit, and thecomparator may also be provided in one of the pen tip side and theeraser side. In this case, the pen tip side and the eraser side may beswitched between each other, and thus the respective pieces of penpressure information may be detected in a time division manner.

Although in this embodiment, the data representing the directionoriented to the tablet is transmitted earlier than the pen pressuredata, the transmission order may be reversed.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, foreign patents, andforeign patent publications referred to in this specification and/orlisted in the Application Data Sheet are incorporated herein byreference, in their entirety. Aspects of the embodiments can bemodified, if necessary to employ concepts of the various patents andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A position detector comprising: a position indicator including asignal generator, the signal generator being configured to continuouslytransmit a detection signal to a tablet as a position signal and tointermittently transmit the detection signal to the tablet as anon-positional signal, the position indicator further including anamplifying circuit and a switch configured to activate the amplifyingcircuit in synchronization with completion of each continuoustransmission of the detection signal as the position signal and todeactivate the amplifying circuit after a fixed period of time; and thetablet configured to determine a position on its surface pointed to bysaid position indicator by detecting the continuously-transmitteddetection signal, and to determine non-positional information regardingthe position indicator by detecting the intermittently-transmitteddetection signal, wherein said position indicator further includesposition indicator control circuitry configured to control the positionindicator to: (i) receive, during said fixed period of time, anindicator control signal via the signal generator from said tablet andamplify the received indicator control signal via the amplifying circuitselectively activated by the switch and deactivate the amplifyingcircuit after said fixed period of time, and (ii) based on the receivedand amplified indicator control signal, select one type ofnon-positional information from among multiple types of non-positionalinformation regarding the position indicator, and (iii) transmit theselected one type of non-positional information regarding the positionindicator as the non-positional signal to said tablet via the signalgenerator, wherein said tablet includes tablet control circuitryconfigured to control the tablet to: (a) continuously receive thedetection signal from said position indicator to determine thepositional information and to intermittently receive the detectionsignal from said position indicator to determine the non-positionalinformation, and (b) determine a timing at which the continuoustransmission of the detection signal is completed, and (c) transmit,during said fixed period of time, the indicator control signal to saidposition indicator synchronously with the determined timing.
 2. Theposition detector according to claim 1, wherein the indicator controlsignal transmitted from said tablet is transmitted as digitalinformation expressed in a plurality of bits.
 3. The position detectoraccording to claim 1, wherein the multiple types of non-positionalinformation include pen pressure information detected by the positionindicator.
 4. The position detector according to claim 1, wherein themultiple types of non-positional information include identification (ID)information of the position indicator.
 5. The position detectoraccording to claim 1, wherein the multiple types of non-positionalinformation include slider status information detected by the positionindicator.
 6. The position detector according to claim 1, wherein saidtablet control circuitry of the tablet are configured to control thetablet to (c) transmit the indicator control signal to said positionindicator after determining that the continuous transmission of thedetection signal from the position indicator as the positional signal isstopped.
 7. The position detector according to claim 6, wherein saidtablet control circuitry of the tablet determine that the continuoustransmission of the detection signal from the position indicator as thepositional signal is stopped when detecting that a voltage correspondingto the detection signal that has been continuously generated for adefined period of time falls below a threshold.
 8. The position detectoraccording to claim 1, wherein the position indicator includes a powersource comprising a battery.
 9. The position detector according to claim1, wherein said position indicator control circuitry of the positionindicator are configured to control the position indicator to (i)receive the indicator control signal from the tablet after stopping thecontinuous transmission of the detection signal to the tablet as thepositional signal.
 10. The position detector according to claim 1,wherein said position indicator control circuitry of the positionindicator are further configured to control the position indicator to:(iv) cease transmission of the detection signal to the tablet when notdetecting the indicator control signal during a defined period of timeafter stopping the continuous transmission of the detection signal tothe tablet as the positional signal.
 11. The position detector accordingto claim 1, wherein said position indicator control circuitry of theposition indicator are further configured to control the positionindicator to: (iv) cease transmission of the detection signal to thetablet when continuously not detecting the indicator control signal fromthe tablet for a defined period of time.
 12. A position detectorcomprising: a position indicator including a signal generator, thesignal generator being configured to continuously transmit a detectionsignal to a tablet as a positional signal and to intermittently transmitthe detection signal to the tablet as a non-positional signal, theposition indicator further including an amplifying circuit and a switchconfigured to activate the amplifying circuit in synchronization withcompletion of each continuous transmission of the detection signal asthe position signal and to deactivate the amplifying circuit after afixed period of time; and the tablet configured to determine a positionon its surface pointed to by said position indicator by detecting thecontinuously-transmitted detection signal, and to determine thenon-positional information regarding the position indicator by detectingthe intermittently-transmitted detection signal, wherein said tablet isconfigured to transmit, during said fixed period of time, an indicatorcontrol signal to the position indicator to initiate intermittenttransmission of the detection signal from said position indicator, andwherein said position indicator is configured to receive, during saidfixed period of time, the indicator control signal via the signalgenerator and to amplify the received indicator control signal via theamplifying circuit selectively activated by the switch, to deactivatethe amplifying circuit after said fixed period of time, and to start theintermittent transmission of the detection signal as the non-positionalsignal to the tablet via the signal generator according to the receivedand amplified indicator control signal.
 13. A position indicatorcomprising: a signal generator configured to continuously transmit adetection signal to a tablet as a position signal and to intermittentlytransmit the detection signal to the tablet as a non-positional signal,an amplifying circuit and a switch configured to activate the amplifyingcircuit in synchronization with completion of each continuoustransmission of the detection signal as the position signal and todeactivate the amplifying circuit after a fixed period of time, andposition indicator control circuitry configured to control the positionindicator to: (i) receive, during said fixed period of time, anindicator control signal via the signal generator from said tablet andamplify the received indicator control signal via the amplifying circuitselectively activated by the switch and deactivate the amplifyingcircuit after said fixed period of time; and (ii) determine whether ornot a strength of the received and amplified indicator control signal isequal to or larger than a predetermined level; and (iii) based on thereceived and amplified indicator control signal determined to be equalto or larger than the predetermined level, select one type ofnon-positional information from among multiple types of non-positionalinformation regarding the position indicator; and (iv) transmit theselected one type of non-positional information regarding the positionindicator as the non-positional signal to said tablet via the signalgenerator.
 14. The position indicator according to claim 13, wherein themultiple types of non-positional information include one or more of penpressure information detected by the position indicator, identification(ID) information of the position indicator, and slider statusinformation detected by the position indicator.
 15. The positionindicator according to claim 13, which further includes a power sourcecomprising a battery.
 16. The position indicator according to claim 13,wherein said position indicator control circuitry are configured tocontrol the position indicator to (i) receive the indicator controlsignal from the tablet after stopping the continuous transmission of thedetection signal to the tablet as the positional signal.
 17. Theposition indicator according to claim 13, wherein said positionindicator control circuitry are further configured to control theposition indicator to: (v) cease transmission of the detection signal tothe tablet when not detecting the indicator control signal during adefined period of time after stopping the continuous transmission of thedetection signal to the tablet as the positional signal.
 18. Theposition indicator according to claim 13, wherein said positionindicator control circuitry are further configured to control theposition indicator to: (v) cease transmission of the detection signal tothe tablet when continuously not detecting the indicator control signalfrom the tablet for a defined period of time.
 19. A position indicatorcomprising: a signal generator configured to continuously transmit adetection signal to a tablet as a position signal and to intermittentlytransmit the detection signal to the tablet as a non-positional signal,an amplifying circuit and a switch configured to activate the amplifyingcircuit in synchronization with completion of each continuoustransmission of the detection signal as the position signal and todeactivate the amplifying circuit after a fixed period of time, apressure detecting circuit configured to detect a pressure applied to atip of the position indicator to generate pressure informationindicative of the detected pressure, and position indicator controlcircuitry configured to control the position indicator to: (i) receive,during said fixed period of time, an indicator control signal via thesignal generator from said tablet and amplify the received indicatorcontrol signal via the amplifying circuit selectively activated by theswitch and deactivate the amplifying circuit after said fixed period oftime; and (ii) determine whether or not a strength of the received andamplified indicator control signal is equal to or larger than apredetermined level; and (iii) based on the received and amplifiedindicator control signal determined to be equal to or larger than thepredetermined level, select one type of non-positional information fromamong multiple types of non-positional information regarding theposition indicator including the pressure information; and (iv) transmitthe selected one type of non-positional information regarding theposition indicator as the non-positional signal to said tablet via thesignal generator.
 20. The position indicator according to claim 19,further comprising: a slider switch provided on an exterior surface ofthe position indicator; and a slider detecting circuit configured todetect slider information indicative of a positional status of theslider switch relative to the exterior surface of the positionindicator, wherein the multiple types of non-positional informationregarding the position indicator that may be transmitted to the tabletvia the signal generator includes the slider information.